Decoupled Uplink and Downlink Access in Heterogeneous Networks

Data centric UEs are currently not only demanding more capacity from wireless networks, but also service oriented Quality of Service (QoS) and comparable Quality of Experience (QoE) in both Downlink (DL) and Uplink (UL). With the introduction of internet of things, machine to machine communications, cloud services and the widely-used social media, UEs and devices in general are increasingly more content generators than they were before. As a consequence, the new generations of mobile communications must devise strategies that improve the device’s overall experience. Adding intelligence into the Media Access Control (MAC) and Radio Resource Control (RRC) layers has shown significant improvements in terms of data rate and fairness. However, the non-constant QoE of UEs along the cell area motivates to increase the number of serving eNBs by adding cells of shorter coverage, bringing the network closer to the UE. This change in the deployment allows to further improve the network capacity by enabling better load balancing among the cells and eliminating coverage holes. However, this new paradigm of system design brings with it significant open challenges to ensure a correct operation such as: backhaul improvement, mobility and interference management, cell association and UL/DL relationship. One of the key issues when moving towards a user or service centric network is to provide the mobile network with sufficient flexibility to select the serving cell that better suits the device or service requirements. To this direction, Downlink and Uplink Decoupling (DUDe) goes one step further, and allows the user to independently transmit and receive to and from different base stations. Essentially, DUDe breaks the hard and classical constraint of cell selection based on downlink received power, and provides the network with the flexibility to associate users to different eNBs in the DL and UL. This chapter describes in detail the DUDe technique. First, Section 8.2 goes through the main challenges HetNets must face in terms of radio planning and interference management, and reviews the potential solutions to address these problems.